The Vatican must remove all child sexual abusers from their posts and turn them over to the police, the United Nations children's rights watchdog said on Wednesday.

The UN Committee on the Rights of the Child urged the Holy See to "immediately remove all known and suspected child sexual abusers from assignment and refer the matter to the relevant law enforcement authorities for investigation and prosecution purposes".

In a hard-hitting report, the committee said that the Catholic Church was still failing to do enough to live up to its stated commitment to stamp out child abuse by priests and lay employees, including in schools.

It underlined its "deepest concern about child sexual abuse committed by members of the Catholic churches who operate under the authority of the Holy See, with clerics having been involved in the sexual abuse of tens of thousands of children worldwide".

"The Committee is gravely concerned that the Holy See has not acknowledged the extent of the crimes committed, has not taken the necessary measures to address cases of child sexual abuse and to protect children, and has adopted policies and practices which have led to the continuation of the abuse by and the impunity of the perpetrators," it added.

It blasted the practice of transferring child abusers from parish to parish within countries, and even across borders, in an attempt to cover up their crimes and remove them from the clutches of justice authorities.

"The practice of offenders' mobility, which has allowed many priests to remain in contact with children and to continue to abuse them, still places children in many countries at high risk of sexual abuse, as dozens of child sexual offenders are reported to be still in contact with children," it said.

The report followed a landmark hearing last month during which members of the committee - made up of 18 independent human rights experts from around the globe - grilled senior Churchmen and repeatedly called into question the Vatican's resolve.